1. WUR coexistence with existing power save mode
Month Year
doc.: IEEE yy/xxxxr0
July 2017
WUR coexistence with existing power save mode
Date:
Authors:
Woojin Ahn et al., WILUS
John Doe, Some Company

2. July 2017
Abstract
Discussions on WUR mode transition along with existing power save mode
Follow-up issues for better integration with unscheduled power save protocol
Woojin Ahn et al., WILUS

3. Power save mechanisms in 802.11
July 2017
Power save mechanisms in
power save mechanism defines two Power Management modes:
Active mode: The STA remains in the awake state
Power save mode: The STA enters the awake state to receive or transmit frames. The STA remains in the doze state otherwise.
Normal PS mode(PS-poll), U-APSD
After successful frame exchange with PM subfield indication, STA may change its PM mode
AP shall maintain for each associated STA a Power Management status
Woojin Ahn et al., WILUS

4. New power save mechanisms in TGba
July 2017
New power save mechanisms in TGba
TGba introduces additional power save mechanism
STA may transit its WUR mode between on/off
STA may use WUR mode request frame or element for state transition
In WUR mode, STA only receives WUP and may wake up its PCR
In the mentioned 3 modes, possible actions and expected reactions of STA could be different
In order to integrate WUR with PCR power save mechanism seamlessly, it is important to define how STA maintains and transits its state among them
Woojin Ahn et al., WILUS

5. WUR mode transition with PM mode (1)
July 2017
WUR mode transition with PM mode (1)
1) Including WUR mode as another PM mode
One transition diagram consists of three modes
Active, PS, WUR
State transition diagram might become more complicated
Transition conditions for each mode must be further defined
May require additional signaling for each transition
Require to define additional PM mode in the baseline
As well as corresponding behaviors
Option (1) is not preferable
Implementation complexity
Requiring many changes to existing PM mode behavior
Woojin Ahn et al., WILUS

6. WUR mode transition with PM mode (2)
July 2017
WUR mode transition with PM mode (2)
2) Maintaining WUR mode separate from PM mode
AP maintains PM mode and WUR mode of each associated STA independently
STA might use both PS mode and WUR mode simultaneously
Similar with WNM sleep mode
Option 2) seems more beneficial, since:
State transition diagram is simpler
No additional signaling methods are necessary for mode transition
Little or no modification is required for baseline PM mode
Woojin Ahn et al., WILUS

7. Further consideration on option (2)
July 2017
Further consideration on option (2)
Applying option (2), we may reuse the baseline power save spec text as it is
The baseline requires a non-AP STA in PS mode to wake up periodically
Beacon period for unscheduled power save protocols
Normal power save mode, U-APSD
Scheduled service period for scheduled power save protocols
WNM sleep, TWT
As the periodic wake-up events can be replaced by WUP transmission, we can relieve the wake-up requirements
In order to save more power
For example, non-AP STA using an unscheduled power save protocol, it may not wake-up to receive Beacon frame
Woojin Ahn et al., WILUS

8. July 2017
Follow-up issues for better integration with unscheduled power save protocol
WUR allows AP to wake-up a non-AP STA to listen when it has a buffered BU
AP doesn’t have to wait until the STA wakes up by itself
Low latency can be achieved while STA saves more power
However, unless a wake-up STA responds with an expected frame, AP may not deliver the buffered BU immediately
In normal PS mode and U-APSD, AP can deliver buffered BUs for a STA in PS mode only when it receives a specific frame
PS-poll (normal PS mode) or trigger frame (U-APSD)
In such case low latency gain of WUR may not be achieved
And STA will consume more power
Woojin Ahn et al., WILUS

9. July 2017
WUR with normal PS mode
For a STA using normal PS mode, AP delivers buffered BU only when it receives PS-poll from the STA
If the STA transmits a frame other than PS-poll in response to unicast WUP, it cannot retrieve buffered BU
STA might wait until the next beacon reception to retrieve BUs
Nevertheless the intends to respond with PS-poll, it should transmit it using AC_BE
AC_BE is defined to to reduce the likelihood of collision following a Beacon frame
It is better to respond with PS-poll when a STA using normal PS mode receives unicast WUP
In such case, the transmission of PS-poll could have higher priority BU
Latency
WUP
Ack
Beacon
Ack or single BU
QoS Data or Null
PS-poll
Woojin Ahn et al., WILUS

10. July 2017
WUR with U-APSD
A STA using PS mode may choose which ACs use U-APSD
The ACs using U-APSD are regarded as trigger-enabled/delivery-enabled AC
Other ACs use normal PS mode
According to AP operation during the CP
“For a STA using U-APSD, the AP transmits one BU destined for the STA from any AC that is not delivery-enabled in response to PS-Poll frame from the STA.”
“The AP transmits BUs destined for the STA and using delivery-enabled ACs during an unscheduled SP.”
Upon the reception of a unicast WUP, the STA may not know for which AC it should retrieve buffered BUs
Latency and power consumption will increase until an appropriate retrieving frame is sent
As well as unnecessary channel occupation
U-APSD
Normal PS
U-APSD
Normal PS VO VI BE BK VO VI BE BK
BU for VO
BU for BE
Latency
Latency
WUP
Ack
Ack BU
WUP
Ack
QoS Null EOSP:1
SP early termination
Ack or single BU
PS-poll
trigger frame
trigger frame
Ack
PS-poll
SP start
Woojin Ahn et al., WILUS

11. July 2017
Proposal (1)
We can consider including some information in unicast WUP to optimize non-AP STA’s wake-up behavior
E.g., AC bitmap (4 bits), U-APSD/PS-poll flag
Assuming AC bitmap is included in each unicast WUP
indicating presence of buffered BU for each AC
STA can adapt its response behavior with given information
It can choose a proper response type and access class
Improving efficiency of wake-up event without modification of legacy PS mode
Normal PS
U-APSD
Normal PS VO VI BE BK VO VI BE BK
BU for BE
BU for VO
Latency
Latency
WUP
Ack BU
WUP
Ack
BU (EOSP:0)
BU (EOSP:0)
AC bitmap
AC bitmap
PS-poll
trigger frame (AC_VO)
Ack
Ack
SP start
Channel Access using AC_VI
STA might choose its response type and access class
Woojin Ahn et al., WILUS

12. July 2017
Proposal (2)
If a WUR non-AP STA uses U-APSD, all ACs shall be set to trigger/delivery-enabled AC
To avoid ambiguity without having information in WUP
STA will respond with the expected frame if it is willing to retrieve buffered BUs
Normal PS
U-APSD VO VI BE BK VO VI BE BK
BU for BE
BU for VO
Latency
Latency
WUP
Ack BU
WUP
Ack
BU (EOSP:0)
BU (EOSP:0)
PS-poll
trigger frame (AC_VO)
Ack
Ack
SP start
Woojin Ahn et al., WILUS

13. July 2017
Summary
We have discussed WUR mode transition along with existing power save mode
Maintaining WUR mode and PM mode separately
Follow-up issues for better integration with unscheduled power save protocol
1) Adding information in unicast WUP
E.g., AC bitmap
2) Additional condition for a WUR non-AP STA using unscheduled power save protocol
Woojin Ahn et al., WILUS

14. Strawpoll 1 Do you support the following?
July 2017
Strawpoll 1
Do you support the following?
A non-AP STA may use both PS mode and WUR mode simultaneously
If the non-AP STA is using one of unscheduled power save protocols (e.g., normal PS mode, U-APSD), it may not wake-up to receive Beacon frame
Y/N/A
Woojin Ahn et al., WILUS

15. Strawpoll 2 Do you support the following?
July 2017
Strawpoll 2
Do you support the following?
Unicast wake-up packet shall contain an information to assist wake up response behavior of the destined STA
E.g., AC information of buffered BUs for the destined STA
Y/N/A
Woojin Ahn et al., WILUS

16. Strawpoll 3 Do you support the following?
July 2017
Strawpoll 3
Do you support the following?
If a WUR non-AP STA uses U-APSD, all ACs shall be set to trigger/delivery-enabled AC
Y/N/A
Woojin Ahn et al., WILUS